In printing of textiles, it is common to use a printing paste containing a dye and a thickener. Among the commonly used thickeners are biological polymers and chemically modified biological polymers, such as alginate, galactomannan, starch and carboxymethyl cellulose. But also synthetic thickeners can be used.
With most printing methods, the polymer and excess dye must be removed by washing with water after the fixation of the print. Generally, a large amount of water is required for complete removal of excess dye due to the risk of back-staining during the process, i.e. redeposit on the fabric of already dissolved dye, which may cause unwanted dye transfer during laundering by the consumer. The risk of back-staining is significant in the early stages of the rinsing and/or at high temperatures, especially when the polymer is quickly solubilized.
After dyeing of fabric or yarn, the excess dyestuff, after the fixation, has to be removed by washing with water. Generally, a large amount of water is required for complete removal of excess dye, and during washing the backstaining of released dyestuff will result in an insufficient wet fastness unless the washing is repeated several times.
When garments sewn of differently dyed fabrics are subjected to a wet treatment, e.g. for desizing or so-called "stone-washing" of denim, there is a risk of dye transfer.
In a conventional process the printed or dyed textile is first rinsed with cold water, then washed at high temperature with the addition of a suitable additive to decrease backstaining like PVP. The process is repeated until satisfactory amount of dyestuff (and thickener) have been removed. A polyvinyl pyrrolidone (PVP) can be added as a retarder to reduce backstaining during hot washing, but this compound does not bleach the dye and is relatively expensive. The waste water from a conventional process tends to be strongly coloured and may represent a disposal problem.